In a typical radio frequency (RF) plasma generator arrangement, a high power RF generator produces a RF wave at a preset frequency, such as 13.56 MHz, that is applied to a plasma chamber via a power conduit. Because an impedance mismatch typically exists between the RF power source and the plasma chamber, an impedance matching network is placed between the RF generator and the plasma chamber. Plasma chambers characteristically operate non-linearly which, in combination with line losses in the impedance matching network, results in less than all of the output power of the RF generator reaching the plasma chamber. A sensor functions as a combined voltage and current probe, referred to as a V/I probe, is typically placed in close proximity to the power input to the plasma chamber to detect the voltage and current of the RF wave as it enters the plasma chamber. Accurately measuring the voltage and current in close proximity to the chamber as possible provides an indication of the quality of the plasma process. This in turn yields better control of the etching or deposition characteristics for a silicon wafer or other workpiece in the chamber.
In order to obtain accurate measurements, the V/I probe is calibrated under predetermined and strictly controlled conditions. Calibration occurs at the place of manufacture or factory prior to being sent into the field for installation. In order to further assure accuracy, a sensor or V/I probe is bundled into a RF metrology system. The RF metrology system includes a sensor or V/I probe, a cable, and an analysis unit. This entire RF metrology system is calibrated at the factory prior to being sent into the field for installation and use. When RF metrology components in the field need repair or replacement, the entirety of the RF metrology system must be removed from the field installation. The metrology system is returned to the manufacturer or authorized repair facility, where one or more components of the RF metrology system are repaired or replaced. The repair facility then recalibrates the entire RF metrology system and returns the repaired RF metrology system to the field for reinstallation and use.
While the above process does enable reuse of the components of the RF metrology system, if any one portion of the RF metrology system needs repair, whether it be the sensor, the cable, or the analysis unit, the entirety of the system must be removed in the field. No present system enables the replacement or repair of a single component of the metrology system in the field. This can significantly increase the cost and delay of returning the metrology system to operation once it has been determined that anyone component of the metrology system requires repair.
In addition to repair issues, present systems to not provide for convenient upgrading of RF metrology components. Conventional RF metrology systems face similar issues with respect to upgrades as they do for repair or replacement. When it is desired to replace one or a number of components of the RF metrology system with different or improved components, present systems require that the entirety of the system be removed so that the replacement component can be installed and the system recalibrated. This adds to the cost of upgrading components of an RF metrology system and can adversely impact downtime of the plasma chamber. Further yet, it may at times be preferable to install a passive sensor component into a RF system and install an analysis module at a later time. Conventional RF systems, however, would require that the RF metrology components be removed and recalibrated in order to add the analysis component at a later time. This requires disturbing the RF path in order to calibrate which is generally undesirable.